COMPMID-3314: Enable OpenMP in the reference tests

Change-Id: I05b5fedb998317144e0dd13a6377a97207b27f46
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/3024
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/validation/reference/Floor.cpp b/tests/validation/reference/Floor.cpp
index b011a16..21fa1c9 100644
--- a/tests/validation/reference/Floor.cpp
+++ b/tests/validation/reference/Floor.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018 ARM Limited.
+ * Copyright (c) 2017-2020 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -42,6 +42,9 @@
     SimpleTensor<T> dst{ src.shape(), src.data_type() };
 
     // Compute reference
+#if defined(_OPENMP)
+    #pragma omp parallel for
+#endif /* _OPENMP */
     for(int i = 0; i < src.num_elements(); ++i)
     {
         dst[i] = std::floor(src[i]);